In the Phase Alternating Line (PAL) television encoding system, chroma phase errors with regularity are generated when the chroma signal of the television signal is demodulated. That is, in each field, the chroma value of each pixel in each scan line comprises an error, and the errors of adjacent scan lines are alternately positive and negative, as shown in FIG. 1A. In FIG. 1A, the fields are denoted in f, and f0 to f3 represent four consecutive fields, wherein f0 and f2 are even fields, and f1 and f3 are odd fields. L0, L1, L2 . . . are in sequence scan lines of the frame. As shown in FIG. 1, the even fields and the odd fields comprise even and odd numbers of scan lines respectively. In the same field, the errors in adjacent scan lines are equal in magnitude but opposite in sign. For example, in the even field f0, the errors of scan lines L0, L2, L4, L6 . . . are +E0, −E0, +E0, −E0 . . . respectively. Further, the errors of scan lines in different fields can be different. For example, the errors of scan lines in the fields f0 and f1 are ±E0 and ±E1 respectively.
The fields in FIG. 1A are de-interlaced to produce the frames, denoted in F, in FIG. 1B. The frame F0 is formed by de-interlacing the fields f0 and f1, and the frame F1 is produced by de-interlacing the fields f2 and f3. After the fields in FIG. 1A are de-interlaced, the errors of neighboring even scan lines (such as L0 and L2, or L2 and L4) and the errors of neighboring odd scan lines (such as L1 and L3 or L3 and L5) in each frame are equal in magnitude and opposite in sign.
FIG. 2 is a schematic diagram showing a conventional structure for processing a television signal. As shown in FIG. 2, a video decoder 21 decodes a received television signal, and transmits the decoded television signal to the de-interlacing circuit 22. Finally, the signal is scaled by a scaler 23 for output. In the prior structure of FIG. 2, the errors of the PAL television signal described above are eliminated by the video decoder 21. In order to eliminate the errors, one or two additional scan line buffers are required in the video decoder 21 to temporarily store the scan lines of fields. As a result, both hardware cost and time for signal processing are increased.